Presently, it is known to use high temperature reinforced composites as bearings, bushings, and the like, Such composites are typically formed by laminating layers of fibrous cloth to each other by means of an appropriate thermosetting resin. Such resin impregnates the cloth, surrounding the fibers thereof, and is cured by the application of heat for a given period of time. Of particular interest herein are composites wherein the fibers of the cloth are formed of carbon, glass, teflon, and the like, and wherein the resin is polymeric.
The manufacturing of a bearing or bushing from the laminates discussed above typically begins with the formation of an appropriate preform comprising one or more layers of cloth formed in a tubular fashion and impregnated with the polymeric resin. The preform is then used as the base for finishing the bearing or bushing. Generally, a single preform is sufficient for finishing the product, though the building up of additional composite layers is also contemplated.
Previously, the preforms of interest were made by stretching a length of tubular braid over a rigid tubular mandrel. Several such braid-covered mandrels would then be placed into a holding fixture. The retained mandrels and holding fixture would then be placed into a vacuum chamber containing a pool of resin of sufficient depth to coat a given length of the braid-covered mandrels. The mandrels would be suspended above the resin and within a vacuum to remove all air from the cloth or braid. After such air was removed, the cloth or braid-covered mandrels were immersed in the pool of resin for a period of time sufficient to allow the cloth or braid to saturate with the resin. The mandrels were then removed from the resin pool and held thereover for a period of time to allow excess resin to drip back into the pool. Each mandrel was then pulled through a wiper ring to remove all resin except that which would pass through the ring while being maintained upon and between the fibers of the braid. The removed resin, along with any loose fibers from the braid, were allowed to fall into the resin pool. The resin-impregnated tubular braids maintained on the tubular mandrels were then B-staged to make the resin rigid and removed from the mandrel. The rigid tube was then cut into predetermined lengths to serve as a preform for the subsequent steps in the production process of the bearing, bushing, or the like. Those skilled in the art will appreciate that the B-staging operation serves to remove a substantial amount of solvent from the resin, typically through the application of heat, to transform the resin from fluid to solid.
The prior art process presented above has been found to be slow and labor intensive. Further, it is given to contamination and waste of the costly resin, since the entire resin pool is subjected to a plurality of tubular braids upon the mandrels. Loose fibers and contaminates from each of the braids therefore access the entirety of the resin pool. Dependent upon the degree of contamination experienced, it is not uncommon for the entire pool of resin to be discarded following the dipping process.
The prior art has further demonstrated some inconsistencies in the impregnation of the cloth or fabric weave with the resin. The simple dipping and wiping process described above does not necessarily assure that complete penetration of the fibrous cloth by the resin is achieved. Additionally, exposure of the resin pool to vacuum and ambient air gives rise to evaporation of resin solvent, changing the solids content of the resin and decreasing the ability of the resin to uniformly impregnate the fabric weave.